A study of Pt/WO42−/ZrO2 catalyst deactivation in the hydroisomerization of heptane and a heptane–benzene mixture

Abstract

The dynamics of the catalytic properties of a Pt/WO₄²⁻/ZrO₂ catalyst (17 mol % WO₄²⁻) in the hydroisomerization of heptane and a heptane–benzene mixture as a function of reaction time and temperature has been studied. It has been found that the heptane conversion decreases in the initial reaction period (within 2 h) and the isohexane selectivity symmetrically increases at 170–280°C, with the benzene hydrogenating activity decreasing at 250°C and higher temperatures. The observed changes in catalytic properties are attributed to the partial deactivation of both the acid and hydrogenation components of the catalyst. X-ray photoelectron spectroscopy has revealed the formation of carbon deposits on the catalyst surface; the structure of the deposits is determined by the reaction medium composition. The composition of the products formed on the catalyst after heptane hydroisomerization is mostly represented by aliphatic polymers of the “poly-С_хН_y” type, which are capable of blocking the active sites that catalyze the cracking reactions. The addition of benzene to heptane has led to the formation of graphite-like carbon deposits; this feature is apparently responsible for a decrease in both the acidity and hydrogenation activity of the catalyst. The phase state and textural characteristics of the catalysts are stable under the isomerization reaction conditions.